EP0713113A1 - Optical transmitting and receiving device - Google Patents

Abstract

The transmission and reception device has a transmission element (LD) supported by a first carrier (T1), a reception element (PD) and a transmission fibre (Fs) supported by a third carrier (T3) and an intermediate carrier (T2) between the first and third carriers. The surfaces of the carriers are provided with recesses and V-grooves via anisotropic etching, with at least one mirror surface provided for each of the outer carriers. The third carrier is transparent to the light wavelength provided by the transmission element, with a monitoring diode (MD) provided at the surface of the first carrier located in a recess (V2) in the surface of the second carrier.

Description

The invention relates to an optical transmitting and receiving device according to the preamble of patent claim 1.

In an optical transmission and reception device, a transmission fiber must be coupled to a transmission element, usually a laser diode, and to a photodiode as the reception element. The transmit and receive signals are simultaneously transmitted in the opposite direction in the transmission fiber. The transmit and receive signals are separated at the same wavelength using a beam splitter and at different wavelengths using a wavelength-selective splitter. In order to obtain the lowest possible coupling losses, the fiber must be optimally coupled to both the laser diode and the receiving diode. To couple a laser to a single-mode fiber, a beam transformation must be carried out by both because of the different beam characteristics. An image with one or two lenses is usually used for this. The required magnification ratio M is approximately three to five, depending on the ratio of the mode field diameters of the laser and the fiber. Tolerances in the position of the laser are compensated for by an active adjustment of the fiber. The adjustment range required for this is larger in the lateral direction, ie transverse to the beam direction, by the factor M than the lateral tolerance range of the laser and in the axial direction by the factor M². The adjustment of the fiber to the laser also influences the adjustment of the fiber to the photodiode, so that, in particular, a small-area photodiode is used for higher frequencies is suitable, must also be actively adjusted to the fiber.

From DE 39 14 835 C1 an arrangement for coupling an optical waveguide to an optical transmitting or receiving element is known.

An adjustment in the plane lateral to the optical axis is achieved in that the optical waveguide and the optical transmitting or receiving element are fixed on different carriers, the carrier surfaces of which are displaceable on one another and that the light beam is reflected by two reflections each on a mirror plane on a carrier Optical fiber arrives at the optically active element or vice versa. A lateral adjustment is carried out by moving the carrier. The carrier which carries the transmitting or receiving element can consist of a substrate and a part applied thereon, which has a continuous opening through which the light beam passes. The arrangement can be used in all transmission systems with optical fibers, in duplexers with light coupling in or out. In the case of coupling to a transmission element, a reception element can be provided on the carrier with the fiber.

Starting from this prior art, it is an object of the invention to provide an optical transmitting and receiving device in which the adjustment effort is reduced and assembly is simplified.

The object is achieved by an invention with the features of claims 1 and 2.
Advantageous further developments are specified in the subclaims.

In order to reduce the adjustment effort and to simplify the assembly, an optical transmission and reception device is proposed, in which only an active and automatable adjustment process is required, and in which the assembly of the optical components is considerably simplified by precise and inexpensive mounting structures.

• Fig. 1 einen Schnitt durch eine erfindungsgemäße Anordnung mit Monitordiode auf dem Träger der Laserdiode;
• Fig. 1a einen Schnitt durch eine erfindungsgemäße Anordnung mit Monitordiode auf dem Träger der Übertragungsfaser;
• Fig. 2 Aufbau zur Justage der Anordnung;
• Fig. 3 erfindungsgemäße Anordnung, wobei der dritte Träger mit seiner Stirnseite zum ersten Träger ausgerichtet ist und
• Fig. 4 erfindungsgemäße Anordnung, deren dritter Träger gegenüber der Anordnung nach Fig. 1 vertikal und horizontal gespiegelt ist.

Embodiments of the invention are described with reference to the drawings. Show it:

• 1 shows a section through an arrangement according to the invention with a monitor diode on the carrier of the laser diode.
• 1a shows a section through an arrangement according to the invention with a monitor diode on the carrier of the transmission fiber;
• Fig. 2 structure for adjusting the arrangement;
• Fig. 3 arrangement according to the invention, wherein the third carrier is aligned with its end face to the first carrier and
• Fig. 4 arrangement according to the invention, the third carrier is mirrored vertically and horizontally compared to the arrangement of FIG. 1.

. Zur Erleichterung der Positionierung wird die Laserdiode bei der Montage an die Fußlinien von mindestens zwei rechtwinklig zueinander liegenden Seitenflächen angelegt. Eine dieser Seitenflächen S1 liegt dabei vor der Stirnfläche des Lasers mit der Lichtaustrittsfläche LA. Die Seitenfläche S1 ist verspiegelt, so daß das aus dem Laser austretende Lichtbündel L1 schräg nach oben reflektiert wird. Der zunächst waagerecht austretende Mittenstrahl des Bündels schließt nach der Reflexion an der Seitenwand S1 einen Winkel $${\text{γ}}_{\text{11}}\text{= 2*α - 90° = 19,5°}$$

mit der Normalen der Oberfläche des Trägers T1 ein. Über dem Träger T1 ist ein zweiter Träger T2 angebracht, der für die Wellenlänge λ₁ des Laserlichtes transparent ist.
Beispielsweise kann dieser zweite Träger ebenfalls aus Silizium bestehen. Es ist aber auch ein anderes transparentes Material möglich, das mikromechanisch strukturierbar ist wie beispielsweise ein photolitographisch strukturierbares Glas. Auf der Unterseite des Trägers T2 wird in dem Bereich, in dem das Lichtbündel L1 auftrifft eine Linse Li angebracht. Diese Linse kann vorteilhafterweise eine planar aufgebrachte Fresnellinse oder eine holographische Linse sein. Es sind aber auch andere Linsenarten möglich, wie zum Beispiel eine Kugellinse, die in einer mikromechanisch geformten Vertiefung sitzt, oder eine durch Trockenätzen erzeugt Linse. Außerdem ist in der Unterseite des Trägers T2 eine Vertiefung V2 angebracht, damit Platz bleibt für Bonddrähte Bd und Leiterbahnen Lb zur Kontaktierung der Laserdiode LD und für weitere optische oder optoelektronische Bauelemente, die auf der Oberseite des Trägers T1 montiert sind. Hier ist eine Monitordiode MD zur Kontrolle der Laserleistung angebracht.
Die Linse Li wandelt das zunächst divergente Lichtbündel L1 in ein konvergentes Bündel um. Infolge der Lichtbrechung an der Grenzfläche des Trägers T2 wird der Mittelstrahl des Lichtbündels unter dem Winkel $${\text{γ}}_{\text{12}}{\text{= arcsin((n}}_{\text{o}}{\text{/n}}_{\text{2}}{\text{)*sin(γ}}_{\text{11}}\text{))}$$

gebrochen, wobei n_o der Brechungsindex im Raum der Vertiefung V1 und n₂ der Brechungsindex im Träger T2 ist.A first exemplary embodiment of the solution according to the invention is shown in FIG. 1. In a first carrier T1, which consists of monocrystalline silicon, anisotropic etching produces a depression V1 which has a flat bottom B1, on which a laser diode LD is mounted. The side surfaces of the depression have an inclination angle of owing to the anisotropic etching process $\text{α = arctan (}\sqrt{\text{2nd}}\text{) = 54.7 °}$

. To facilitate positioning, the laser diode is attached to the base lines of at least two side surfaces that are at right angles to each other. One of these side surfaces S1 lies in front of the end surface of the laser with the light exit surface LA. The side surface S1 is mirrored, so that the light bundle L1 emerging from the laser reflects obliquely upwards becomes. The center beam of the bundle, which initially emerges horizontally, closes an angle after reflection on the side wall S1 $${\text{γ}}_{\text{11}}\text{= 2 * α - 90 ° = 19.5 °}$$

with the normal of the surface of the carrier T1. Above the carrier T1, a second carrier T2 is attached, which is transparent to the wavelength λ₁ of the laser light.
For example, this second carrier can also consist of silicon. However, it is also possible to use a different transparent material that can be micromechanically structured, such as a photolithographically structured glass. A lens Li is attached to the underside of the carrier T2 in the area in which the light bundle L1 strikes. This lens can advantageously be a planar Fresnel lens or a holographic lens. However, other types of lenses are also possible, for example a spherical lens which is seated in a micromechanically shaped depression, or a lens produced by dry etching. In addition, a recess V2 is provided in the underside of the carrier T2, so that there remains space for bond wires Bd and conductor tracks Lb for contacting the laser diode LD and for further optical or optoelectronic components which are mounted on the top of the carrier T1. Here, a monitor diode MD is attached to control the laser power.
The lens Li converts the initially divergent light bundle L1 into a convergent bundle. As a result of the refraction of light at the interface of the carrier T2, the central beam of the light beam is at an angle $${\text{γ}}_{\text{12th}}{\text{= arcsin ((n}}_{\text{O}}{\text{/ n}}_{\text{2nd}}{\text{) * sin (γ}}_{\text{11}}\text{))}$$

broken, where n _{o is} the refractive index in the space of the depression V1 and n₂ is the refractive index in the carrier T2.

If the carrier T2 made of silicon with a refractive index n₂ = 3.4777 and n _o = 1 for air, then γ₁₂ = 5.5 °.

wobei β₃ der Brechungswinkel an der Stirnfläche S31 mit $${\text{β}}_{\text{3}}{\text{= arcsin((n}}_{\text{o}}{\text{/n}}_{\text{3}}\text{)*sin(90°-α))}$$

ist, gegen die Flächennormale der Substratoberfläche von T3 in das Silizium hineingebrochen. Dabei ist n_o der Brechungindex in der V-Nut V31 und n₃ = 3,4777 der Brechungsindex im Siliziumträger T3. Mit n_o = 1 für Luft erhält man β₃ = 9,6° und γ₂₁ = 64,3°. Das Lichtbündel L2 trifft auf die Seitenfläche S31 der Vertiefung V31 unter einem Einfallswinkel von $${\text{α}}_{\text{3}}{\text{= 180° -2*α - β}}_{\text{3}}\text{= 61,0°.}$$

On the top of the carrier T2, the light beam is broken back in the original direction γ₂. A further carrier T3 is attached there, which, like the carrier T1, likewise consists of single-crystal silicon. Two wells V31 and V32 are anisotropically etched in this carrier T3. The depression V31 is a V-groove for receiving the transmission fiber Fa. The width of this V-groove is expediently so large that the bottom surface line of the fiber comes to lie just in the plane of the underside of T3. The end face S3 of the V-groove is coated with a wavelength-selective filter Fi1. This filter is designed so that the transmission wavelength λ₁ reflects and the reception wavelength λ₂ is transmitted. The transmitted light bundle L1 is reflected on the end face S31 inclined at the angle α again in the horizontal direction and coupled into the transmission fiber Fa. The receiving light bundle L2 emerging from the transmission fiber with the wavelength λ₂ penetrates the filter Fi1 and becomes at the boundary to the silicon at an angle $${\text{γ}}_{}$$$${}_{\text{21}}{\text{= α + β}}_{\text{3rd}}\text{,}$$

where β₃ the angle of refraction on the end face S31 with $${\text{β}}_{\text{3rd}}{\text{= arcsin ((n}}_{\text{O}}{\text{/ n}}_{\text{3rd}}\text{) * sin (90 ° -α))}$$

is broken into the silicon against the surface normal of the substrate surface of T3. Here, n _{o is} the refractive index in the V-groove V31 and n₃ = 3.4777 the refractive index in the silicon carrier T3. With n _o = 1 for air, one obtains β₃ = 9.6 ° and γ₂₁ = 64.3 °. The light bundle L2 strikes the side surface S31 of the depression V31 at an angle of incidence of $${\text{α}}_{\text{3rd}}{\text{= 180 ° -2 * α - β}}_{\text{3rd}}\text{= 61.0 °.}$$

ist, wird das Lichtbündel L2 unter dem Winkel $${\text{γ}}_{\text{22}}{\text{= α}}_{\text{3}}\text{- α = 6,3°}$$

gegen die Flächennormale der Trägeroberfläche gebrochen. Der Winkel γ₂₂ ist kleiner als α_g, so daß das Lichtbündel L2 auf der Oberfläche des Siliziumträgers T3 austreten kann. An der Austrittstelle des Lichtbündels L2 wird die Empfangsdiode PD montiert. Die Position für die Photodiode ergibt sich aus den oben genannten Winkeln, dem Abstand der beiden Vertiefungen V31 und V32 voneinander und mit geringer Abhängigkeit von der Dicke des Trägers T3. Die Position der Lichtaustrittsfläche von L2 hängt dagegen nicht von der axialen Position der Faser Fa in der V-Nut V31 ab. Die Position der Lichtaustrittsfläche kann daher relativ zu den mikromechanisch erzeugten Vertiefungen V31 und V32 durch Marken oder Anschläge gekennzeichnet werden. Diese Marken oder Anschläge können durch photolithographische Technik sehr genau zu den Vertiefungen V31 und V32 ausgerichtet werden. Durch laterale Verschiebung des Trägers T3 relativ zum Träger T2 ist eine laterale Justage der Faser Fa relativ zum Bildpunkt des Sendelichtbündels L1 möglich. Auch eine eventuell erforderliche axiale Justage der Faser durch Verschieben der Faser in der V-Nut V31 ist möglich, ohne daß die Position der Lichtaustrittsfläche des Empfangslichtbündels L2 dadurch geändert wird. Die Aufgabe, die Position der Photodiode zum Empfangslichtbündel unabhängig von der Justage der Faser zum Sendelichtbündel zu halten wird also durch die beschriebene erfindungsgemäße Anordnung erreicht. Dabei ist weiter sehr vorteilhaft, daß alle optoelektronischen Bauteile planar montiert werden können.Since this angle α₃ is greater than the critical angle of total reflection at the silicon / air transition from $${\text{α}}_{\text{G}}{\text{= arcsin (n}}_{\text{O}}{\text{/ n}}_{\text{3rd}}\text{) = 16.7 °}$$

is the light beam L2 at the angle $${\text{γ}}_{}$$$${}_{\text{22}}{\text{= α}}_{\text{3rd}}\text{- α = 6.3 °}$$

broken against the surface normal of the carrier surface. The angle γ₂₂ is smaller than α _g , so that the light bundle L2 can emerge on the surface of the silicon carrier T3. The receiving diode PD is mounted at the exit point of the light bundle L2. The position for the photodiode results from the above-mentioned angles, the distance between the two depressions V31 and V32 from one another and with little dependence on the thickness of the carrier T3. The position of the light exit surface of L2, however, does not depend on the axial position of the fiber Fa in the V-groove V31. The position of the light exit surface can therefore be identified by marks or stops relative to the micromechanically generated recesses V31 and V32. These marks or stops can be aligned very precisely with the depressions V31 and V32 using photolithographic technology. Lateral displacement of the carrier T3 relative to the carrier T2 enables a lateral adjustment of the fiber Fa relative to the pixel of the transmitted light bundle L1. A possibly necessary axial adjustment of the fiber by shifting the fiber in the V-groove V31 is possible without changing the position of the light exit surface of the received light beam L2. The task of keeping the position of the photodiode relative to the received light beam independent of the adjustment of the fiber relative to the transmitted light beam is thus achieved by the arrangement according to the invention described. It is also very advantageous that all optoelectronic components can be mounted planar.

gegen die Flächennormale auf die Oberfläche des Trägers T3 auf. Dieser Winkel ist aber größer als der Grenzwinkel der Totalreflexion α_g = 16,7°, so daß das direkte Störlicht vom Sender nicht in die Empfangsdiode gelangen kann.Another advantage of the solution according to the invention is that a very high near crosstalk attenuation can be achieved. A high near crosstalk attenuation is necessary so that the transmitted signal from the laser does not hit the receiving diode located near the transmitter due to insufficient directional separation and disturbs the reception of weak useful signals. Filter layers generally have a limited ability to separate different wavelengths. Therefore, a small proportion of the transmitted light bundle L1 will also penetrate the filter layer S31. The beam path of this stray light is shown in dashed lines as S1 '. This light beam hits at an angle $${\text{γ}}_{\text{13}}{\text{'= α - β}}_{\text{3rd}}\text{= 45.2 °}$$

against the surface normal on the surface of the carrier T3. However, this angle is larger than the critical angle of the total reflection α _g = 16.7 °, so that the direct interference light from the transmitter cannot reach the receiving diode.

In a variant of the first exemplary embodiment, the filter Fi1 is designed such that a small part of the transmitted light still penetrates the filter while the largest part is reflected. This light beam L1 'penetrating the filter is used according to the invention as a control signal. The monitor diode MD 'is then not mounted on the carrier T1 but in a recess V33 on the carrier T2. This is shown in dashed lines in FIG. 1a.

For the lateral active adjustment of the fiber to the transmitted light bundle L1, the carrier T3 is expediently inserted in a metal flange Fl3, the edge surface of which is on the side wall Sw of a housing designed as a flange surface Fl1 G rests in which the supports T1 and T2 are mounted. After the optimal coupling position has been reached, the flange surfaces Fl3 and Fl2 are fixed in their position relative to one another, for example by laser welding spots LS. The carrier T2 can serve as a translucent, hermetically sealed cover of the housing G. An additional hermetically sealed window Fe can also be used between the supports T2 and T3. (See Fig. 2).

In a second exemplary embodiment of the solution according to the invention, the carrier T3 is not aligned with its underside but with its end face to the carrier T2.
The second exemplary embodiment according to the invention is shown in FIG. 3. The carriers T1 and T2 are constructed as in the first exemplary embodiment. The fiber Fa is again guided in a V-groove V31 in a carrier T3 and is also axially adjustable in this V-groove. The end face S31 is also covered with a wavelength select filter layer Fi2. In contrast to the filter layer F11 in the first exemplary embodiment, the filter layer Fi2 is transparent for the transmission wavelength λ₁ and reflective for the reception wavelength λ₂. The emerging at an angle of γ₁₁ = 19.5 ° from the beam T2 light beam L1 strikes the side wall S31 an anisotropically etched from the opposite side in the carrier T3 depression V32, the part opposite the side wall S32, for example by sawing, has been removed is. Since the two side surfaces S32 and S31 are parallel to each other, the transmitted light bundle S1 is offset in parallel by the double refraction and then hits the transmission fiber Fa. The carrier T3 must be inclined at an angle γ₁₁ = 19.5 ° to the surface normal of the carrier T2 be. For this purpose, it is installed at an angle in the flange F3.

A third embodiment of the solution according to the invention is shown in FIG. 4. Here, the carrier T3 is constructed similarly to the first exemplary embodiment, however mirrored vertically and horizontally compared to the first embodiment. As in exemplary embodiment 2, the filter layer Fi2 must be transparent for the transmission wavelength and reflective for the reception wavelength. As in exemplary embodiment 2, the photodiode PD for the received signal is mounted in the region above the end face of the V-groove V31. As in embodiment 2, the advantage here is that the path between the end face of the fiber and the photodiode is very short, which results in a small beam expansion and therefore allows a very small-area photodiode that is suitable for high frequencies. The direction angle γ₁₂ of the beam in the carrier T2 is 5.5 ° for the carrier material silicon and the direction angle γ₂₂ of the beam in the carrier T3 is 6.3 °. The difference in angle of 0.8 ° results in a coupling loss of approx. 0.1 dB and is tolerable in most applications. The angle γ₁₂ can be corrected by the position of the lens center of the lens Li relative to the surface S1. The longer light path in the carrier T3 for the transmitted light bundle compared to the first exemplary embodiment has to be compensated for by a corresponding thickness of the carrier T2.

A very important aspect regarding the costs of using laser diodes in transmitter modules or transmitter and receiver modules is that the laser diodes can be checked as early as possible during the manufacturing process. While electrical tests can be carried out before separation, optical tests can often only be carried out after installation on individual subsinks or even on the finished module. With the assembly method according to the invention, the laser diodes can be tested for their optical functions at a very early stage and with great benefits. For this purpose, the laser diodes are mounted in the depressions V1 of a carrier substrate T1 produced in large-scale use before this carrier substrate is separated into individual carriers. To this In this way, the optical properties for a large number of laser diodes can be tested together. The carrier T2 with the lens Li is also produced in large-scale use for many individual modules and all lenses are assembled together with the lasers in a single adjustment and assembly process. Passive adjustment using marks or adjustment-free assembly using micromechanically structured stops is possible here. The depressions V2 in the carrier T2 are designed so that the optoelectronic and electronic components such as the laser diode LD, the monitor diode MD or electronic modules (not shown here) for controlling the laser are hermetically sealed. After the common connection of the carrier substrates T1 and T2, these are separated by sawing or breaking at micromechanically generated predetermined breaking lines. The position of the sawing or breaking lines is such that the position of the depressions V1 and V2 and the lenses Li are not touched.

The monitor diode MD can also be mounted on the underside or top of the supports T2 or T3, with corresponding recesses being provided in the adjacent support. A further lens Lim can be provided on the carrier T2 for coupling the monitor diode.

Claims (3)

Optical transmission and reception device with a transmission element (LD), which is fixed on a first carrier (T1), with a receiving element (PD) and a transmission fiber (Fs), which are fixed on a third carrier (T3) and with a second Carrier (T2), which is located between the first and the third carrier (T1, T3), with V-grooves and depressions in the carriers (T1, T2, T3), which are produced by anisotropic etching, with at least one mirror surface each of the outer supports (T1, T3), characterized in that the third support (T3) is transparent to light with the wavelength of the light emitted by the transmitting element (LD), that a monitor diode (MD) is provided on the surface of the first carrier (T1) is mounted in a recess of the second carrier (T2). Optical transmission and reception device with a transmission element (LD), which is fixed on a first carrier (T1), with a receiving element (PD) and a transmission fiber (Fs), which are fixed on a third carrier (T3) and with a second Carrier (T2), which is located between the first and the third carrier (T1, T3), with V-grooves and depressions in the carriers (T1, T2, T3), which are produced by anisotropic etching, with at least one mirror surface each of the outer supports (T1, T3), characterized in that the third support (T3) is transparent to light with the wavelength of the light emitted by the transmitting element (LD), that a monitor diode (MD) is provided on the surface of the second carrier (T2) is mounted in a recess of the third carrier (T3). Optical transmitting and receiving device according to claim 1, characterized in that the optical axis of the transmission fiber (Fa) encloses an angle in the range between 50 ° and 90 ° with the surface of the carrier (T1, T2).

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